Hitherto, methods of manufacturing a silicone-type graft copolymer have been categorized into methods in which active groups are formed by drawing hydrogen from lower alkyl groups bonded to silicon atoms of the silicone and then organic polymers are grafted to the active groups, and a method in which silicone having the active groups is previously manufactured and then the organic polymers are grafted to the active groups.
In the former case, hydrogen must be drawn from silicone, and therefore suitable methods and conditions must be employed. For example, the ability for drawing hydrogen, the grafting efficiency and the molecular weight of the organic polymer grafted to the organic peroxide are affected by the type and the quantity of the organic peroxide and the reaction temperature. However, it is difficult to adequately control the foregoing factors.
In the latter case, silicone having active groups and living polymers obtainable from anion polymerization are allowed to react with each other so that the silicone type graft copolymer can be obtained. However, due to excessive complication of the structure using the anion polymerization, unsatisfactory range in selecting the polymerizable monomer for use in the anion polymerization, high manufacturing cost and difficulty involved in the operation the latter method has been unsatisfactory as a commercial manufacturing method.
On the other hand, a method (hereinafter referred to as a "macromonomer method"), in which high-molecular monomers each having polymerizable functional groups, such as double bonds, are copolymerized with other copolymer monomers and which is able to manufacture the graft polymers, has attracted attention. In this case, the foregoing method has generally been performed by means of solution polymerization in which both high-molecular monomers and monomers to be copolymerized with the high-molecular monomers are dissolved in an organic solvent and they are polymerized or by means of suspension polymerization caused to proceed in a water-based solvent. However, the solution-type graft polymer cannot satisfy the needs of the times to prevent pollution and save resources, while the graft polymer obtainable from the suspension polymerization encounters phase separation into a liquid phase and a solid phase, making it difficult to use in liquid form as a water-based dispersion. Therefore, an emulsion type graft polymer, which can be used in place of the foregoing graft polymer and which is composed of emulsified dispersions each having a small particle size, has been earnestly sought. Although there are only a few methods for manufacturing the graft polymer by means of the macromonomer method in which the water-based emulsification polymerization is performed, there are the following proposals.
For example, Japanese Patent Laid-Open No. 3-163103 has suggested a method for manufacturing a graft polymer emulsion comprising the steps of: dissolving high-molecular monomers each having radical polymerizable functional groups and an oil soluble radical polymerization initiator in another vinyl monomer which is copolymerizable with the high-molecular monomer; emulsifying and dispersing, in a water-based medium, the obtained solution under the presence of an emulsifier composed of an alkali metal sulfosuccinate or another sulfonic acid or alkali metallic salt sulfate type anion surface active agent and a nonion surface active agent having an HLB value of 10 or more; and raising the temperature to copolymerize the high-molecular monomers and the other vinyl monomers.
However, the foregoing method requires that the high-molecular monomer and another copolymerizable monomer, which is copolymerized with the high-molecular monomer, have some compatibility. Therefore, high-molecular monomers, such as silicone high-molecular monomers, that have excessively poor compatibility with the other copolymerizable monomer to be copolymerized, are omitted from the scope of the foregoing invention. If the substances to be copolymerized with each other are not compatible, a problem rises in that aggregated blocks (called grids) are formed in great quantities during the polymerization. There also arises another problem in that the purity is low because large quantities of polymers that have not been grafted are contained therein.
On the other hand, Japanese Patent Laid-Open No. 1-284513 discloses an acryl-type emulsion composition manufactured by a usual emulsification polymerizing method using low molecular weight silicone type high-molecular monomers, the number n of repetitions of structural units of which is 20 or less, the obtained composition being free from grids and having greater vapor penetration resistance and waterproofness than the conventional acrylic emulsion. However, the repellency and the separation characteristics and the like that are the inherent characteristics of the silicone type polymers cannot be obtained. What is worse, a problem of unsatisfactory stability has obstructed the practical use of the foregoing composition.
It has not always easy to have a silicone type high-molecular monomer, which has no compatibility with the other copolymerizable monomer used, react sufficiently and cause all of the characteristics of the silicone polymer based on that reaction to be exhibited. That is, the rate of reaction can be raised by only reducing the molecular weight of the silicone type high-molecular monomer. Furthermore, the molecular weight of the silicone type high-molecular monomer must be raised in order to cause the silicone to exhibit its characteristics. It has been difficult to find a good balance between the foregoing factors. That is, it has been very difficult for the silicone type high-molecular monomer having a high molecular weight to be formed into a highly polymerized copolymer at an excellent rate of reaction.
As described above, another problem arises in that aggregations of polymers (called "grids") are easily formed at the time of the emulsification polymerization in the system using the silicone type high-molecular monomer. Furthermore, the stability of the obtainable water-based copolymer emulsion has been unsatisfactory. As a result, a satisfactory method has not been achieved yet.
The present invention is directed to the manufacture of a water-based copolymer emulsion using a silicone type high-molecular monomer, and an object thereof is to establish a method of manufacturing a water-based silicone type graft copolymer emulsion exhibiting satisfactory stability, and excellent repellency and separating characteristics, in which silicone having radical polymerizable functional groups each having a large molecular weight is used to cause the silicone component to sufficiently exhibit its characteristics while maintaining a high rate of reaction, and preventing the formation of grids which create problems at the time of emulsification polymerizing reactions of high-molecular monomers having large molecular weights.